Optimizing the manufacturing conditions of CaO/Ca(OH)₂ for thermochemical energy storage utilizing a bubbling fluidized bed to reduce particle degradation

Thermal energy storage in the temperature range from 400 °C to 600 °C has been the focus of technological development in recent years. The thermochemical material system CaO/Ca(OH)₂ has been identified as promising due to its high storage capacity, abundant availability, and nontoxicity. When used in a fluidized bed, its low heat conductivity can be overcome, and the process scalability is increased. However, particle breakage due to chemical and mechanical stress during the cyclization operation can lead to defluidization and, with it, the end of the storage operation. This study investigates the influence of the process conditions during the production of the storage material CaO/Ca(OH)₂ from calcination of CaCO₃ on the particle stability in a lab-scale fluidized bed reactor (d_i = 80 mm, H = 350 mm, 850 °C, 4 bar). Mild conditions (T_calc< 750 °C) extend the material‘s lifetime from 25.5 to 40.5 cycles. The increase in lifetime is related to the increase in particle density and decrease of the mean pore diameter. The mild conditions are possible due to the catalytic effect of H₂O on the reaction rate of the calcination, resulting in the reduction of the reactions’ apparent activation energy from 205.0 kJ/mol (N₂-atmosphere) to 157.1 kJ/mol.